In connection with the design of certain nuclear reactors, it is desirable and sometimes required to provide fuel rods which have been internally pressurized. It is desirable to have pressurized fuel rods to between 200 and 700 psig with an inert gas, preferably helium.
Generally, the approach for pressurizing a fuel rod has been to load the fuel rod with the nuclear fuel and then to pressurize it. Obviously, however, this requires providing appropriate access to the interior of the rods after the fuel has been loaded in order to apply the necessary pressure. This has been usually accomplished by a number of methods, one of which includes providing end caps having preformed access openings therein for application of the pressure once the end caps have been secured to the fuel rod. This technique, however, has been found deficient for a variety of reasons, some of which are listed in prior art U.S. Pat. No. 3,774,010. The patent also discloses another technique for pressurizing a loaded fuel rod which includes locating an end of the rod within a pressure chamber and then by means of a laser beam, causing an access hole to be formed in the end of the fuel rod, and then proceeding with the pressurization thereof. Verification that the fuel rod has been properly pressurized heretofore has been accomplished by waiting for a sufficient amount of time to elapse to ensure that the pressure in the chamber has come to equilibrium with the fuel rod. This practice has proven to be deficient since it does not provide an accurate indication of when pressurization of the rod has been completed.
The present invention provides a system and method for determining when pressurization of the fuel rod has been completed, as well as providing a means for determining when each of the activities associated and usually preceding such pressurization have occurred and when they have been completed.